1. Field of the Invention
The present invention is directed to a light emitting diode driving device and a driving method thereof, and in particular to a light emitting diode device for use in a display and a driving method thereof.
2. Description of the Related Art
Because of the good characteristics of light emitting diodes (LEDs) such as low power consumption and low operating temperature, LEDs have been widely used in various applications.
For example, many small size panels use LEDs connected in series as backlights. Many backlights of cell phones or personal digital assistants (PDAs) also use LEDs for illumination. In addition, owing to the halgon free requirement of the European League, the new generation of LED driving devices and driving methods is needed.
Backlights of many portable products have a backlight adjusting function. That is, in some conditions such as in certain circumstances without outer power supply, illumination of backlights is adjustable to decrease the power consumption to increase the lifetime of batteries. However, current LED driving methods have following disadvantages:
The driving current flowing through LEDs is fixed and not adjustable with various conditions. Since the amount of the driving current determines the luminance, current-fixing driving scheme further limits the convenience in different applications.
The driving current is fixed to the current of maximum luminance. Driving LEDs by the maximum luminance current in all conditions makes LEDs operate in a lower efficiency region.
Since current LED driving methods have the deficiencies above, an improved LED driving method is needed.